Figure 102

Changes in renal function during pregnancy. Marked renal hemo-dynamic changes are apparent by the end of the first trimester. Both the glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) increase by 50%. ERPF probably increases to a greater extent, and thus, the filtration fraction is decreased during early and mid pregnancy. Micropuncture studies performed in animals suggest the basis for the increase in GFR is primarily the increase in glomerular plasma flow [1]. The average creatinine level and urea nitrogen concentration are slightly lower than in pregnant women than in those who are not pregnant (0.5 mg/d and 9 mg/dL, respectively). The increased filtered load also results in increased urinary protein excretion, glucosuria, and aminoaciduria. The uric acid clearance rates increase to a greater extent than does the GFR. Hypercalciuria is a result of increased GFR and of increases in circulating 1,25-dihydroxy-vitamin D3 in pregnancy (absorptive hypercalciuria). The renin-angiotensin system is stimulated during gestation, and cumulative retention of approximately 950 mEq of sodium occurs. This sodium retention results from a complex interplay between natriuretic and antinatriuretic stimuli present during gestation [2].

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